Barbula has been much reduced in size. K. Saito (1975) presented cogent reasons for recognizing Didymodon as distinct. Characters of importance in distinguishing Barbula are: axillary hairs almost always entirely of hyaline cells; leaf adaxially usually deeply grooved along the costa; distal laminal cell papillae rough, knobby, obscuring the lumens, and protuberant along the distal laminal margins; costa usually excurrent as a sharp mucro or an apiculus of one or more clear cells; peristome is long and twisted, and as Saito (1975) pointed out, Barbula has gemmae generally larger than those of Didymodon. The three sections are represented in the flora area: sect. Barbula, including B. unguiculata and B. orizabensis; sect. Convolutae Bruch & Schimper (Streblotrichum P. Beauvois), including B. amplexifolia, B. convoluta, and B. indica; and sect. Hydrogonium (Müller Hal.) K. Saito [Hydrogonium (Müller Hal.) A. Jaeger], including B. bolleana. For many taxa previously long-held in Barbula, see 16. Didymodon.

Abaxial costa surface cells doubly prorate (i.e., with both ends of rectangular superficial cells protruding) near apex, often with coarse mammillae in rows across the costa; leaf base widened but not sheathing.

Costa percurrent or ending before the apex; leaf apex entire or apiculate by a smooth or weakly papillose conical cell; specialized asexual reproduction when present by tubers on proximal rhizoids, or if by axillary gemmae then gemmae large and single in the axils; perigoniophores very short-stemmed.